One form of a wireless communication system is a mobile communication system such as a mobile phone system. In the mobile communication system, transmission speed varies depending on the transmission speed per unit frequency and a frequency band. The transmission speed for each base station apparatus increases as the realizable transmission speed per unit frequency and the usable frequency band increase. The transmission speed for each terminal apparatus increases as the transmission speed per assigned unit frequency or unit time, the frequency band, and the time period increase.
FIG. 29 is a diagram of a configuration of the mobile communication system. As depicted in FIG. 29, the mobile communication system includes a terminal apparatus 1, a base station apparatus 2, network connecting equipment 3, and a communication network 4. The terminal apparatus 1 is connected to the base station apparatus 2 wirelessly. The base station 2 is connected to the network connecting equipment 3 by cable. The base station apparatus 2 converts and relays wireless and wired signals, manages wireless and wired lines, and controls communication with the terminal apparatus 1.
The base station apparatus 2 forms a cell or a cell-divided sector as an area in which to communicate with the terminal apparatus 1. The network connecting equipment 3 is connected to the communication network 4 by cable. The network connecting equipment 3 relays wired signals between multiple base station apparatuses 2 and between the base station apparatus 2 and the communication network 4, manages the wired lines thereof, and further manages the state of the terminal apparatus 1.
Schemes for communication between the terminal apparatus 1 and the base station apparatus 2 include Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), Orthogonal Frequency Division Multiple Access (OFDMA), among others. The base station apparatus 2, according to the communication system to be employed, assigns to the terminal apparatus 1, a frequency, a time, a code, etc. for performing communication. The base station apparatus 2 assigns an appropriate modulation and coding scheme according to the wireless quality at the terminal apparatus 1.
Ordinarily, with FDMA, TDMA, OFDM, etc., to avoid interference in the vicinity of a border of adjacent cells or sectors (hereinafter, cell(s), etc.), usable frequency is divided into plural frequencies and a different frequency is assigned to each adjacent cell, etc. However, with such frequency division and assignment, the transmission speed between the terminal apparatus 1 and the base station apparatus 2 decreases because the frequency band of each cell, etc. narrows.
Therefore, a frequency assignment scheme has been proposed that is designed to improve the transmission speed by superimposing a divided frequency commonly over all cells, etc. (see, e.g., Japanese Laid-Open Patent Publication No. 2004-159345). FIG. 30 is a diagram for describing this frequency assignment scheme and FIG. 31 is a diagram depicting the relationship of the frequency, the time, and the transmission power of a signal transmitted from the base station apparatus in each cell, etc. depicted in FIG. 30. As depicted in these figures, the usable frequency is divided into four frequencies and cell A11 is assigned frequency fA different from the frequencies of adjacent cell B12 and cell C13. Frequency fD common among all cells is superimposed over this frequency fA.
Likewise, the cell B12 and the cell C13 are assigned frequency fB and frequency fC, respectively and the frequency fD is superimposed over each of these frequencies. According to this frequency assignment scheme, a terminal apparatus near the border of a cell, etc., cannot communicate with the base station apparatus using the frequency fD due to interference with adjacent cells, etc. that use the same frequency fD. Therefore, in cell A11, for example, a terminal apparatus near the border of cell A11 communicates with the base station apparatus using the frequency fA. On the other hand, a terminal apparatus near the center of the cell, etc., namely, in an area near the base station (indicated as a steel tower figure) can communicate with the base station apparatus by the frequency fD in addition to the frequency fA.
According to the frequency assignment scheme disclosed in Patent Document 1, since each cell, etc., uses the frequency (fD) common among all cells, etc., in addition to the frequency (fA, fB, or fC) uniquely assigned to each cell, etc., the frequency band assigned to each cell, etc., becomes wider and the transmission speed is improved between the terminal apparatus and the base station apparatus. However, the frequency fD must be established separately.